The present invention relates to a device capable of producing an air stream having a flattened shape in transverse section, particularly for spraying a treatment product over the ground or over plants.
In order to send an air stream laden with treatment product over the ground or over plants, use is usually made of two types of apparatus. A first type (U.S. Pat. No. 3,252,656 to GREENWOOD and U.S. Pat. No. 3,653,130 to PATRICK, and French Patent No. 1 314 453 to BERTHOUD) includes a helical blower which sprays a jet of air with high flow rate and modest speed in the direction of the axis of rotation of its fan. This air jet may be diverted with the aid of appropriate deflectors in order to be converted into an air stream with flattened transverse section but, if it is desired to create a sheet of air in parallel motion of large width, it is necessary to provide several blowers, each having its own deflectors.
A second type of apparatus (U.S. Pat. No. 4,026,469 to FRANKEL and U.S. Pat. No. 2,925,222, SPRENG) for producing an air stream comprises a single centrifugal compressor which delivers air at modest flow rate, at a relatively high pressure. The air thus compressed is conveyed through suitable pipes to nozzles which produce jets of air with high speed and small initial cross-section. The air jets produced, which may be of flattened shape in transverse section and which may all be located in one and the same plane, penetrate the air, and also the foliage of the plants, like daggers, that is to say, the air moves at high speed along the axis of each jet, but this air has an almost zero speed between the jets. This results in poor distribution of the treatment product.
In U.S. Pat. No. 3,164,324 to BRUINSMA, there is described apparatus which contains both a centrifugal compressor and helical blowers. The centrifugal compressor is used merely to produce a jet of air at high speed which is used to shred a jet of treatment liquid into fine droplets, which are injected, with the aid of the same high-speed air jet, along the axis of the air stream created by the helical blower. This complicated solution does not allow the drawbacks of apparatus with helical blowers to be overcome.
UK Patent Application No. 2.227.399 calls upon another technique, which is that of the venturi. According to this technique, a high-speed air jet is injected, by an injector formed of a nozzle or the like, axially at the inlet of a diffuser formed of a convergent-divergent pipe. The air jet imparts its energy to the air located inside the diffuser, so that an air flow with high flow rate and modest speed, similar to the one which a helical blower provides, may be obtained.
In order to obtain an air stream of flattened shape, provision is made, according to the document which has just been quoted, to use either a single diffuser which is straight in transverse section and of long length, fed by a series of injectors mounted on a manifold parallel to the diffuser, or a series of injector-diffuser assemblies, in which each diffuser has a closed, oval or circular cross-section and is associated with a single injector, connected to the manifold by a pipe.
The first solution is known to give good results only in a narrow range of flow rates, and the second solution results in a complex and unwieldy structure, complicated to fit together.
The object of the present invention is to provide a device which affords the performance of a system with several assemblies, each comprising a diffuser with closed cross-section associated with a single injector, and which may at the same time be constructed in a simple and inexpensive fashion.